X-ray absorption spectroscopy has been used to establish polymer formation of Tc(IV) in aqueous solutions of Na+SO42- and Na+Cl-/SO42-. As the molybdenum chemistry show similarities to that of technetium, we used MoO2 as a reference to model our technetium species. Fitting of TcO2·xH2O with this model led to a good correlation with the literature data: (Tc-Tc=2.53 Å, Tc-O=1.87-1.98 Å). In aqueous solution, some polymers are formed regardless to the nature of the media composition: Tc-Tc=2.50±0.02 Å. The general structure is in agreement with a first coordination shell containing 6 O. The modelling shows that, in the first coordination shell, there is no chloride ligand. The observed geometries are close to those found for TcO2·xH2O, hence the unknown aqueous species must be considered as a precursor of the solid technetium dioxide. Combination of these results with XANES led to attribute TcnIVOp(4n-2p)+(H2O)q with n>2 to the species.